1. Field of the Invention
The present invention relates generally to an apparatus and method for controlling the power to components while installing or removing the components for an electronic device while the electronic device is powered.
2. Description of the Related Art
Many electronic devices, such as computers, are equipped with expansion card slots which enable the devices' hardware to be enhanced by insertion of cards which contain additional memory, processors, or other specialized items. Insertion and removal of such cards, whether for the purpose of performing repairs to the cards or merely the purpose of changing the hardware configuration of the computer, generally require that the computer be powered down and turned off during the maintenance period.
However, many computer uses require that the computer remain running continuously, or at least for extended periods of time. In such situations, the computer must not be powered down simply to change the compliment of cards. When a card is inserted or withdrawn while the computer is powered and running, the sharp and sudden change of current through the inductive mother-board power path will induce voltage spikes, which will appear at both the card and the computer. These spikes may often be large enough to cause loss of data, incorrect program execution, or even permanent damage to the delicate hardware components themselves.
Prior attempts to enable cards to be inserted or withdrawn in "power-on" circumstances have proved less than satisfactory. One known technique is the "umbilical cord" method. A typical card is powered via connecting pins at its attaching edge, which engage complimentary members of the card slot's connector device. To use the umbilical cord, each card is adapted with a plug which is wired in parallel with the connecting pins, and before the card is inserted, a technician attaches an umbilical cord to the card. Power can then be gradually brought up on the card via a control device in the umbilical cord, in a slow enough manner to avoid causing spikes. After the card is powered up, it can be inserted into the card slot and the umbilical cord removed.
However, this method leaves the computer's integrity wide open to technician error or neglect. If the technician forgets to attach the cord to the card, and inserts the card, spikes will result and may destroy the system. The technician may also neglect to adjust the umbilical cord's power control device before attaching the cord to the card, with similar results. Extraction of circuit cards from a live system also poses similar hazards.
Another known method involves the use of large, cumbersome, and expensive power control units at each card slot in the computer. Since the card slots themselves are provided with the spike avoidance devices, that method is wastefully expensive. Even unused card slots are equipped with the devices, so unneeded power control units must be purchased with the computer. Since the devices are large and powerconsuming, that method is also wasteful of electricity, as such a system will continually be ready to power up cards which may never be inserted. The addition of devices at the mother-board also substantially increases the impedance of the power path, with a corresponding increase in any spikes which do occur.
It is an object of the present invention to provide an apparatus and method of inserting and removing cards from a computer while the computer is running. It is a further object of the present invention to remove the possibility of human error or neglect, to ensure that spikes are automatically avoided when cards are inserted and withdrawn. It is still a further object to make the present invention neither wasteful nor expensive.